1. Field of the Invention
The present invention generally relates to an illumination system and more particularly to an illumination system for a projection apparatus.
2. Description of Relative Art
Referring to FIG. 1, an illumination system 100 of a conventional liquid crystal on silicon (LCOS) projection apparatus adopting scrolling color recapture (SCR) technology includes a light source 110, a light integration rod (LIR) 120, a color wheel 130, a polarization conversion system (PCS) 140 and a relay lens group 150. The relay lens group 150 includes a plurality of lenses 152, 154 and 156. In addition, the light source 110 is for providing an illumination beam 112 which passes through the LIR 120 and the color wheel 130, followed by being focused to an LCOS panel 50 by the relay lens group 150. The PCS 140 is disposed between the lens 152 and the lens 156, so as to convert the illumination beam 112 into a beam with the same polarization state.
In the prior art, the color wheel 130 is disposed between the LIR 120 and the relay lens group 150. However limited by the mechanism, the color wheel 130 and a light output end 124 of the LIR 120 are unable to be disposed on the object plane of the relay lens group 150, which leads to edge blur problem of a light spot on the LCOS panel 50.
Referring to FIG. 2, generally, considering the system tolerance, an ideal light spot 32 has a size slightly larger than the size of the LCOS panel 50. In fact, a light spot (as shown by the light spot 34) with blur edges is generated. The edges of the light spot 34 may fall on the LCOS panel 50 to cause that the illumination beam 112 is received by the LCOS panel 50 nonumiformly, which degrades the projection imaging quality. In the prior art, in order to avoid the edges of the light spot 36 from falling on the LCOS panel 50, the light spot size is increased (as shown by the light spot 36 in FIG. 2). However, the overfill ratio of the light spot 36 with respect to the LCOS panel 50 in the case is higher, which lowers the light utilization efficiency and the brightness of the projection images.
Referring to FIGS. 1 and 3A, the notation 38 of FIG. 3A represents a light spot formed by the illumination beam projected on the color wheel 130. The color wheel 130 is composed of multiple filters 132 with different colors. During the period from time T1 at which the boundary 133 between two adjacent filters 132 is passing the left end of a horizontal line 39a of the light spot 38 to time T2 at which the boundary 133 is passing the right end of the horizontal line 39a, the horizontal line 39a falls on two filters 132 with two different colors, such that the light with two different colors is transmitted away from the color wheel 130 to the LCOS panel 50, which causes a color mess and affects the color quality of the images. To avoid the color mess, the LCOS panel 50 usually stops image processing during the period from time T1 to time T2, which leads to a loss of image luminance.
Referring to FIG. 3B, similar to the above described, the same problem occurs during the period from time T3 at which the boundary 133 is passing through the right end of another horizontal line 39b of the light spot 38 to time T4 at which the boundary 133 is passing through the left end of the horizontal line 39b. 